PDF readers are available for all operating systems. The book is not an e-book or an on-line course. Anyone using it is best advised to make a hardcopy for reading and to work through practice exercises with pencil and paper.

as a course reader

Instructors using forall x as a textbook are welcome to have the book printed at a local copy center, which may sell it to students for the cost of printing. This is typically more efficient than having every student print it themselves, and copy centers also offer extras like binding.

forall x is a available through Lulu, a print-on-demand publisher. They charge a price that covers printing and shipping. I offer it for individuals who would like a nicely bound hardcopy; for an entire class, the course reader option would probably be more economical.

The raw LaTeX source files are maintained on GitbHub. If you are interested in making changes, you can download the files or fork the project. As an example: I use the arrow for the conditional and the ampersand for conjunction. These are my aesthetic and pedagogical preferences, but perhaps your tastes or curricular needs are different. Changing one line will change the symbols throughout the book, because the logical symbols are defined commands in the style file for the book. E-mail me if are interested in a variant of the book but are daunted by LaTeX.

other formats?

I do not foresee the book ever being available in HTML or as a Word document. Logical notation is is just too hard to represent reliably, and I have no interest in maintaining multiple versions. The license being what it is, you are welcome to convert it to any format you like. If you do, let me know; I will link to you.